It is known that fixed and movable work machines used in industrial and nonindustrial fields use stopping or parking brakes which are actuated by large locking springs and which, once engaged, allow to slow the work machine while it is moving or to keep it stationary safely.
In the normal operation of work machines, the brakes are kept released by means of a hydraulic system provided with jacks which contrast the elastic force of the springs.
By modulating the pressure of the fluid (usually but not exclusively oil) inside the jacks, it is possible to control the resulting force that acts on the brakes and therefore adjust the intensity of the braking force.
This modulation is usually performed by using suitable manually actuated hydraulic valves, wherein the term “manual” references any intervention performed directly by the operator for example by means of a lever, pedal or the like.
Known types of valve are constituted usually by an outer casing provided with ports for connection respectively to a pressurized oil supply pump, to an oil discharge tank and to the brake locking jacks.
A longitudinal seat is formed within the casing and a contoured slider slides therein, allowing to connect to each other the connecting ports, particularly to send pressurized fluid to the jacks and release the brakes, or to discharge the contents into the discharge tank and allow the springs of the brakes to slow/block the work machine.
The slider is moved by means of the actuation lever or pedal in contrast with two springs arranged inside the casing; in detail, a first spring acts directly on the slider and control the pressure of the oil fed to the jacks, while a second spring is designed to load the first spring with a force which is sufficient to deliver the brake release pressure.
When the brakes are engaged and the work machine is stationary, these known types of valve are provided with a bolt which is actuated by a contrast spring and locks rigidly the lever or pedal, prevents accidental release of the brakes, and avoids the onset of potentially dangerous situations.
These traditional types of valve are not free from drawbacks, including the fact that due to the use of two slider contrast springs, one designed to load the other, the force that the operator needs to apply to actuate the lever or pedal is often considerable and therefore said operation in some cases is rather tiring, especially if it is performed several times.
Moreover, in conventional valves the openings for the passage of the fluid within the slider sliding seat are often excessively narrow, allowing, other conditions being equal, the passage of small flow-rates of oil and therefore making the braking system scarcely reactive to the commands imparted by the operator; in practice, this causes difficulties in modulating the braking action.
Moreover, it is noted that the system for engaging the bolt to the lever or pedal is sometimes complicated from a constructive and functional standpoint.